1. Field of the Invention
This present invention generally relates to integrated-optical microsystems and, more particularly, to an integrated-optical microsystem based on organic semiconductors and to a method for manufacturing the same. An integrated-optical microsystem comprises at least two different electronic, photonic and/or micromechanic components arranged on a common substrate. Important examples of such components are monochromatic (laser) or polychromatic (LED) light sources, photodetectors, photovoltaic power generators, p-channel and n-channel field-effect transistors, resistors, capacitors, light-guiding or wave-guiding structures, or derived sensing devices for the measurement of pressure, magnetic or electric fields, chemical or bio-chemical substances, etc. Applications include self-powered posters or business cards, millimeter-thin large-area scanners and electronic paper.
2. Description of Related Art
Known techniques for the fabrication of microsystems rely on hybrid methods for the integration of the different functionalities required. Especially photonic microsystems, in which it is necessary to generate and detect light, consist of sub-systems that are manufactured with very different materials, using different types of technology. Light is generated usually with compound semiconductors such as GaAs, InP or InGaAsP. Light is often detected with inorganic semiconductors such as Si or Ge. Electronic circuits are realized with Si-based technologies such as complementary metal oxide semiconductor (CMOS) or bipolar. Passive optical components such as lenses, prisms or mirrors are realized with glass. Microoptical elements such as microlens arrays or diffractive optical components are fabricated with plastic materials, while the bodies and cases of complete systems are manufactured with metals or plastics.
It is known that passive optical functions can be combined with mechanical functions, using injection molding of polymers to produce so-called “optical monoblocks” (cf. P. Seitz, “Real-time optical metrology for microsystems fabrication”, Proc. SPIE, Vol. 3825, pp 104–110, 1999). These integrated systems combine all passive optical elements (refractive, diffractive, reflective and obstructive) and all mechanical elements for assembly, mounting, and fixing in one piece of polymer that can be fabricated, for example, with a single injection-molding process.
It is also known that photosensitive elements, electronic devices, and circuits can be combined monolithically into “smart pixels” and “smart image sensors”, preferably using silicon (cf. P. Seitz, “Smart Image Sensors: An Emerging Key Technology for Advanced Optical Measurement and Microsystems”, Proc. SPIE, Vol. 2783, pp. 244–255, 1996). Due to the semiconductor properties of silicon it is difficult, however, to generate light within the same material used for the rest of the photosensitive and electronic devices.
The difficulty of generating light with silicon can be overcome by employing compound semiconductors, which make it possible to monolithically integrate photosensitive, photoemissive, analog, and digital electronic elements in so-called optoelectronic integrated circuits (OEICs) (cf. U. Kehrli, D. Leipold, K. Thelen, J. E. Epler, P. Seitz and B. D. Patterson, “Monolithically Integrated-optical Differential Amplifiers for Applications in Smart Pixel Arrays”, IEEE J. Quantum Electronics, Vol. 32 (5), pp. 770–777, 1996).
Another, hybrid approach for overcoming the difficulty of generating light with silicon is described in U.S. Pat. No. 6,307,528 by D. Yap. A silicon substrate contains electronic circuits, and an organic semiconducting layer is deposited on top, with which light can be emitted under control of the underlying electronic circuits.
A hybrid solution for an optical head assembly based on an organic electroluminescent light-emitting array is described in U.S. Pat. No. 6,297,842 by M. Koizumi et al. The electronic circuits are contained in a silicon substrate, on top of which an organic semiconductor is deposited that generates light under control of the underlying circuits. These hybrid elements are then mounted on a printed circuit board to form a complete optical head assembly.
U.S. Pat. No. 5,770,446 by T. Sasaki et al. describes the monolithic combination of laser, optical amplifier, optical waveguide, optical modulator, and optical switch with a suitable selection of inorganic compound semiconductors such as InP and InGaAsP. Devices are formed with a sequence of selective crystal growth processes using demanding metallo-organic vapor phase epitaxy, photolithographic definition of structures, and suitable etching steps.
U.S. Pat. No. 6,228,670 by K. Kudo describes the monolithic combination of a highly integrated array of laser diodes, waveguides, and optical amplifiers. Devices are formed with a sequence of selective crystal growth processes using demanding metallo-organic vapor phase epitaxy, photolithographic definition of structures, and suitable etching steps.
From U.S. Pat. No. 6,300,612 by G. Yu it is known that photosensors based on organic semiconductors can be realized; this reference teaches the fabrication of a two-dimensional arrangement of individually addressable photodiodes. Since no means is foreseen for providing local amplification or electronic buffering, the noise performance of the described organic photosensors must be at least one order of magnitude below the performance of prior-art silicon-based photosensors.